Biochemical, molecular and in silico characterization of arsenate reductase from pH, salt and arsenic tolerant Bacillus thuringiensis KPWP1

The objective of the present study was to characterize aresenate reductase of pH, salt and arsenate tolerant Bacillus thuringiensis KPWP1, isolated from contaminated surface water. Interestingly, it was found that the arsC, arsB and arsR genes involved in arsenate tolerance are distributed in the genome of KPWP1. The inducible arsC gene was cloned, expressed and the purified ArsC protein showed profound enzyme activity with the KM and Kcat values as 25 µM and 0.00119 s− 1, respectively. In silico studies of KPWP1 ArsC revealed that in spite of 19–26% differences in gene sequences, the ArsC proteins of Bacillus thuringiensis, Bacillus subtilis and Bacillus cereus are structurally conserved and KPWP1 ArsC structure is close to nature. Docking and analysis of binding site showed that arsenate ion interacts with three cysteine residues of ArsC of KPWP1and predicts that the ArsC from B. thuringiensis reduces arsenate by using the triple Cys redox relay mechanism.

Rhodanese domain-containing sulfurtransferases: multifaceted proteins involved in sulfur trafficking in plants

Sulfur is an essential element for the growth and development of plants, which synthesize cysteine and methionine from the reductive assimilation of sulfate. Besides its incorporation into proteins, cysteine is the building block for the biosynthesis of numerous sulfur-containing molecules and cofactors. The required sulfur atoms are extracted either directly from cysteine by cysteine desulfurases or indirectly after its catabolic transformation to 3-mercaptopyruvate, a substrate for sulfurtransferases (STRs). Both enzymes are transiently persulfidated in their reaction cycle, i.e. the abstracted sulfur atom is bound to a reactive cysteine residue in the form of a persulfide group. Trans-persulfidation reactions occur when sulfur atoms are transferred to nucleophilic acceptors such as glutathione, proteins, or small metabolites. STRs form a ubiquitous, multigenic protein family. They are characterized by the presence of at least one rhodanese homology domain (Rhd), which usually contains the catalytic, persulfidated cysteine. In this review, we focus on Arabidopsis STRs, presenting the sequence characteristics of all family members as well as their biochemical and structural features. The physiological functions of particular STRs in the biosynthesis of molybdenum cofactor, thio-modification of cytosolic tRNAs, arsenate tolerance, cysteine catabolism, and hydrogen sulfide formation are also discussed.